Modeling the development of pronunciation in infant speech acquisition.

Pronunciation is an important part of speech acquisition, but little attention has been given to the mechanism or mechanisms by which it develops. Speech sound qualities, for example, have just been assumed to develop by simple imitation. In most accounts this is then assumed to be by acoustic matching, with the infant comparing his output to that of his caregiver. There are theoretical and empirical problems with both of these assumptions, and we present a computational model- Elija-that does not learn to pronounce speech sounds this way. Elija starts by exploring the sound making capabilities of his vocal apparatus. Then he uses the natural responses he gets from a caregiver to learn equivalence relations between his vocal actions and his caregiver's speech. We show that Elija progresses from a babbling stage to learning the names of objects. This demonstrates the viability of a non-imitative mechanism in learning to pronounce.

Human muscle spindles act as forward sensory models.

Modern theories of motor control incorporate forward models that combine sensory information and motor commands to predict future sensory states. Such models circumvent unavoidable neural delays associated with on-line feedback control. Here we show that signals in human muscle spindle afferents during unconstrained wrist and finger movements predict future kinematic states of their parent muscle. Specifically, we show that the discharges of type Ia afferents are best correlated with the velocity of length changes in their parent muscles approximately 100-160 ms in the future and that their discharges vary depending on motor sequences in a way that cannot be explained by the state of their parent muscle alone. We therefore conclude that muscle spindles can act as "forward sensory models": they are affected both by the current state of their parent muscle and by efferent (fusimotor) control, and their discharges represent future kinematic states. If this conjecture is correct, then sensorimotor learning implies learning how to control not only the skeletal muscles but also the fusimotor system.

Bycatch provisions in the reauthorized Magnuson-Stevens Act

Bycatch can harm marine ecosystems, reduce biodiversity, lead to injury or mortality of protected species, and have severe economic implications for fisheries. On 12 January 2007, President George W. Bush signed the Magnuson-Stevens Fishery Conservation and Management Reauthorization Act of 2006 (MSRA). The MSRA required the U.S. Secretary of Commerce (Secretary) to establish a Bycatch Reduction Engineering Program (BREP) to develop technological devices and other conservation engineering changes designed to minimize bycatch, seabird interactions, bycatch mortality, and post-release mortality in Federally managed fisheries. The MSRA also required the Secretary to identify nations whose vessels are engaged in the bycatch of protected living marine resources (PLMR’s) under specified circumstances and to certify that these nations have 1) adopted regulatory programs for PLMR’s that are comparable to U.S. programs, taking into account different conditions, and 2) established management plans for PLMR’s that assist in the collection of data to support assessments and conservation of these resources. If a nation fails to take sufficient corrective action and does not receive a positive certification, fishing products from that country may be subject to import prohibitions into the United States. The BREP has made significant progress to develop technological devices and other conservation engineering designed to minimize bycatch, including improvements to bycatch reduction devices and turtle excluder devices in Atlantic and Gulf of Mexico trawl fisheries, gillnets in Northeast fisheries, and trawls in Alaska and Pacific Northwest fisheries. In addition, the international provisions of the MSRA have provided an innovative tool through which the United States can address bycatch by foreign nations. However, the inability of the National Marine Fisheries Service to identify nations whose vessels are engaged in the bycatch of PLMR’s to date will require the development of additional approaches to meet this mandate.

Motor coordination: when two have to act as one.

Trying to pass someone walking toward you in a narrow corridor is a familiar example of a two-person motor game that requires coordination. In this study, we investigate coordination in sensorimotor tasks that correspond to classic coordination games with multiple Nash equilibria, such as "choosing sides," "stag hunt," "chicken," and "battle of sexes". In these tasks, subjects made reaching movements reflecting their continuously evolving "decisions" while they received a continuous payoff in the form of a resistive force counteracting their movements. Successful coordination required two subjects to "choose" the same Nash equilibrium in this force-payoff landscape within a single reach. We found that on the majority of trials coordination was achieved. Compared to the proportion of trials in which miscoordination occurred, successful coordination was characterized by several distinct features: an increased mutual information between the players' movement endpoints, an increased joint entropy during the movements, and by differences in the timing of the players' responses. Moreover, we found that the probability of successful coordination depends on the players' initial distance from the Nash equilibria. Our results suggest that two-person coordination arises naturally in motor interactions and is facilitated by favorable initial positions, stereotypical motor pattern, and differences in response times.